Distributed file deletion and truncation

ABSTRACT

A method for distributed file deletion or truncation, performed by a storage system, is provided. The method includes determining, by an authority owning an inode of a file, which authorities own data portions to be deleted, responsive to a request for the file deletion or truncation. The method includes recording, by the authority owning the inode, the file deletion or truncation in a first memory, and deleting, in background by the authorities that own the data portions to be deleted, the data portions in one of a first memory or a second memory. A system and computer readable media are also provided.

BACKGROUND

Solid-state memory, such as flash, is currently in use in solid-statedrives (SSD) to augment or replace conventional hard disk drives (HDD),writable CD (compact disk) or writable DVD (digital versatile disk)drives, collectively known as spinning media, and tape drives, forstorage of large amounts of data. Flash and other solid-state memorieshave characteristics that differ from spinning media. Yet, manysolid-state drives are designed to conform to hard disk drive standardsfor compatibility reasons, which makes it difficult to provide enhancedfeatures or take advantage of unique aspects of flash and othersolid-state memory.

When deleting or truncating a file, acknowledgement of the deletion ortruncation as soon as possible to the requesting client is desirable. Itis undesirable to have to find all of the “to be deleted” portions of afile, which may be distributed across a storage cluster or storagesystem. Under this mechanism the system must wait until after each ofthe pieces to be deleted is acknowledged, and only then report thedeletion or truncation to the requesting client. It is within thiscontext that the embodiments arise.

SUMMARY

In some embodiments, a method for distributed file deletion ortruncation, performed by a storage system, is provided. The methodincludes determining, by an authority owning an inode of a file, whichauthorities own data portions to be deleted, responsive to a request forthe file deletion or truncation. The method includes recording, by theauthority owning the inode, the file deletion or truncation in a firstmemory, and deleting, in background by the authorities that own the dataportions to be deleted, the data portions in a second memory. In someembodiments, the method operations may be embodied as code on a computerreadable medium.

In some embodiments, a storage system with distributed file deletion andtruncation is provided. The storage system includes a first memory,distributed in the storage system and having RAM (random-access memory)configured to hold metadata and a second memory, distributed in thestorage system and having solid-state storage memory, configured to holddata and metadata. The storage system includes a plurality ofprocessors, configured to record in the first memory, by an authoritythat owns an inode of a file, deletion of the file, responsive to arequest for the deletion of the file. The plurality of processors isfurther configured to record in the first memory, by an authority thatowns an inode of a further file, truncation of the further file,responsive to a request for the truncation of the further file. Theplurality of processors is further configured to have a plurality ofauthorities, each authority of the plurality of authorities owns a dataportion to be deleted, the plurality of processors further configured todelete the data portions in the second memory, in background, resultingfrom the request for the deletion of the file and the request for thetruncation of the further file.

Other aspects and advantages of the embodiments will become apparentfrom the following detailed description taken in conjunction with theaccompanying drawings which illustrate, by way of example, theprinciples of the described embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The described embodiments and the advantages thereof may best beunderstood by reference to the following description taken inconjunction with the accompanying drawings. These drawings in no waylimit any changes in form and detail that may be made to the describedembodiments by one skilled in the art without departing from the spiritand scope of the described embodiments.

FIG. 1 is a perspective view of a storage cluster with multiple storagenodes and internal storage coupled to each storage node to providenetwork attached storage, in accordance with some embodiments.

FIG. 2 is a block diagram showing an interconnect switch couplingmultiple storage nodes in accordance with some embodiments.

FIG. 3 is a multiple level block diagram, showing contents of a storagenode and contents of one of the non-volatile solid state storage unitsin accordance with some embodiments.

FIG. 4 shows a storage server environment, which uses embodiments of thestorage nodes and storage units of FIGS. 1-3 in accordance with someembodiments.

FIG. 5 is a blade hardware block diagram, showing a control plane,compute and storage planes, and authorities interacting with underlyingphysical resources, in accordance with some embodiments.

FIG. 6 is a system and action diagram showing distributed file deletionin a storage system, in accordance with some embodiments.

FIG. 7 is a system and action diagram showing distributed filetruncation in a storage system, in accordance with some embodiments.

FIG. 8 is a flow diagram of a method for distributed file deletion andtruncation, which can be practiced in the storage cluster of FIGS. 1-7and further storage systems, in accordance with some embodiments.

FIG. 9 is an illustration showing an exemplary computing device whichmay implement the embodiments described herein.

DETAILED DESCRIPTION

A storage cluster, and more generally a storage system, described hereincan perform distributed file deletion and/or distributed filetruncation. Various pieces of a file, i.e., data that is distributedthroughout the storage cluster or storage system, are deleted by variousbackground tasks, speeding up the acknowledgment of deletion ortruncation of the file to the requesting client. This acknowledgmentdoes not have to wait until the pieces or portions of the file arephysically deleted. Thus, the system improves response time or latencyfrom when a client makes a request to delete or truncate a file, untilthe storage system acknowledges the file deletion or truncation.

Different pieces of data, or portions of a file, are owned and recordedby authorities under inodes, in storage nodes in the storage system. Theauthority that owns the inode for the file also has responsibility forfile extents for that file in some embodiments. When a client deletes afile (i.e., requests a file be deleted), the request is routed to theauthority that is the owner of the inode for the file. The authoritythat owns the inode for the file records the deletion of the inode as asingle record in NVRAM (non-volatile random-access memory), and recordsa “to do” cleanup record (e.g., a work or cleanup task list or otherdata structure, such as a record of cleanup tasks) in NVRAM. Once thedeletion of the inode is recorded as the single record in NVRAM and the“to do” cleanup is recorded in NVRAM, the authority that owns the inodefor the file reports back to the client acknowledging the file deletion.In the background, cleanup work is picked up in batches shared with allof the authorities that might have pieces of each file. Once theauthority that owns the inode for the file being deleted confirms thatall of the cleanup is completed, that authority deletes the “to do”cleanup task record. Initially, the fact that the inode is deleted isrecorded in NVRAM, and then this record is flushed (e.g., within 30seconds, in some embodiments) to flash (i.e., flash memory in a storageunit), as driven by the processor of the storage node.

When a client truncates a file (i.e., requests a file be truncated), therequest is routed to the authority that is the owner of the inode forthe file. That authority sends or broadcasts the messages to allauthorities that have ownership of pieces of data or portions of thefile (e.g., ranges of segments), and each receiving authority sends asingle message to NVRAM. Each NVRAM record behaves logically like awrite of all zeros. Any read from such an authority will receive backall zeros reported by that authority. An example flow, for someembodiments, is as follows:

-   -   send message to all authorities that may have data for a file    -   each receiving authority writes a truncation record to NVRAM    -   when all responses have been gathered from receiving        authorities, the authority that is the owner of the inode for        the file acknowledges the truncation operation to the client    -   after such acknowledgment, a return of all zeros is guaranteed        to any read of the truncated portion of the file    -   cleaning up data is handled the same way as if an overwrite,        i.e., once NVRAM is flushed to flash, a cleanup operation        overwrites the flash with zeros.

The embodiments below describe a storage cluster that stores user data,such as user data originating from one or more user or client systems orother sources external to the storage cluster. The storage clusterdistributes user data across storage nodes housed within a chassis,using erasure coding and redundant copies of metadata. Erasure codingrefers to a method of data protection or reconstruction in which data isstored across a set of different locations, such as disks, storage nodesor geographic locations. Flash memory is one type of solid-state memorythat may be integrated with the embodiments, although the embodimentsmay be extended to other types of solid-state memory or other storagemedium, including non-solid state memory. Control of storage locationsand workloads are distributed across the storage locations in aclustered peer-to-peer system. Tasks such as mediating communicationsbetween the various storage nodes, detecting when a storage node hasbecome unavailable, and balancing I/Os (inputs and outputs) across thevarious storage nodes, are all handled on a distributed basis. Data islaid out or distributed across multiple storage nodes in data fragmentsor stripes that support data recovery in some embodiments. Ownership ofdata can be reassigned within a cluster, independent of input and outputpatterns. This architecture described in more detail below allows astorage node in the cluster to fail, with the system remainingoperational, since the data can be reconstructed from other storagenodes and thus remain available for input and output operations. Invarious embodiments, a storage node may be referred to as a clusternode, a blade, or a server. Various system aspects are discussed belowwith reference to FIGS. 1-5 and 9. Distributed file deletion andtruncation are described with reference to FIGS. 6-8.

The storage cluster is contained within a chassis, i.e., an enclosurehousing one or more storage nodes. A mechanism to provide power to eachstorage node, such as a power distribution bus, and a communicationmechanism, such as a communication bus that enables communicationbetween the storage nodes are included within the chassis. The storagecluster can run as an independent system in one location according tosome embodiments. In one embodiment, a chassis contains at least twoinstances of both the power distribution and the communication bus whichmay be enabled or disabled independently. The internal communication busmay be an Ethernet bus, however, other technologies such as PeripheralComponent Interconnect (PCI) Express, InfiniBand, and others, areequally suitable. The chassis provides a port for an externalcommunication bus for enabling communication between multiple chassis,directly or through a switch, and with client systems. The externalcommunication may use a technology such as Ethernet, InfiniBand, FibreChannel, etc. In some embodiments, the external communication bus usesdifferent communication bus technologies for inter-chassis and clientcommunication. If a switch is deployed within or between chassis, theswitch may act as a translation between multiple protocols ortechnologies. When multiple chassis are connected to define a storagecluster, the storage cluster may be accessed by a client using eitherproprietary interfaces or standard interfaces such as network filesystem (NFS), common internet file system (CIFS), small computer systeminterface (SCSI) or hypertext transfer protocol (HTTP). Translation fromthe client protocol may occur at the switch, chassis externalcommunication bus or within each storage node.

Each storage node may be one or more storage servers and each storageserver is connected to one or more non-volatile solid state memoryunits, which may be referred to as storage units or storage devices. Oneembodiment includes a single storage server in each storage node andbetween one to eight non-volatile solid state memory units, however thisone example is not meant to be limiting. The storage server may includea processor, dynamic random access memory (DRAM) and interfaces for theinternal communication bus and power distribution for each of the powerbuses. Inside the storage node, the interfaces and storage unit share acommunication bus, e.g., PCI Express, in some embodiments. Thenon-volatile solid state memory units may directly access the internalcommunication bus interface through a storage node communication bus, orrequest the storage node to access the bus interface. The non-volatilesolid state memory unit contains an embedded central processing unit(CPU), solid state storage controller, and a quantity of solid statemass storage, e.g., between 2-32 terabytes (TB) in some embodiments. Anembedded volatile storage medium, such as DRAM, and an energy reserveapparatus are included in the non-volatile solid state memory unit. Insome embodiments, the energy reserve apparatus is a capacitor,super-capacitor, or battery that enables transferring a subset of DRAMcontents to a stable storage medium in the case of power loss. In someembodiments, the non-volatile solid state memory unit is constructedwith a storage class memory, such as phase change or magnetoresistiverandom access memory (MRAM) that substitutes for DRAM and enables areduced power hold-up apparatus.

One of many features of the storage nodes and non-volatile solid statestorage is the ability to proactively rebuild data in a storage cluster.The storage nodes and non-volatile solid state storage can determinewhen a storage node or non-volatile solid state storage in the storagecluster is unreachable, independent of whether there is an attempt toread data involving that storage node or non-volatile solid statestorage. The storage nodes and non-volatile solid state storage thencooperate to recover and rebuild the data in at least partially newlocations. This constitutes a proactive rebuild, in that the systemrebuilds data without waiting until the data is needed for a read accessinitiated from a client system employing the storage cluster. These andfurther details of the storage memory and operation thereof arediscussed below.

FIG. 1 is a perspective view of a storage cluster 160, with multiplestorage nodes 150 and internal solid-state memory coupled to eachstorage node to provide network attached storage or storage areanetwork, in accordance with some embodiments. A network attachedstorage, storage area network, or a storage cluster, or other storagememory, could include one or more storage clusters 160, each having oneor more storage nodes 150, in a flexible and reconfigurable arrangementof both the physical components and the amount of storage memoryprovided thereby. The storage cluster 160 is designed to fit in a rack,and one or more racks can be set up and populated as desired for thestorage memory. The storage cluster 160 has a chassis 138 havingmultiple slots 142. It should be appreciated that chassis 138 may bereferred to as a housing, enclosure, or rack unit. In one embodiment,the chassis 138 has fourteen slots 142, although other numbers of slotsare readily devised. For example, some embodiments have four slots,eight slots, sixteen slots, thirty-two slots, or other suitable numberof slots. Each slot 142 can accommodate one storage node 150 in someembodiments. Chassis 138 includes flaps 148 that can be utilized tomount the chassis 138 on a rack. Fans 144 provide air circulation forcooling of the storage nodes 150 and components thereof, although othercooling components could be used, or an embodiment could be devisedwithout cooling components. A switch fabric 146 couples storage nodes150 within chassis 138 together and to a network for communication tothe memory. In an embodiment depicted in FIG. 1, the slots 142 to theleft of the switch fabric 146 and fans 144 are shown occupied by storagenodes 150, while the slots 142 to the right of the switch fabric 146 andfans 144 are empty and available for insertion of storage node 150 forillustrative purposes. This configuration is one example, and one ormore storage nodes 150 could occupy the slots 142 in various furtherarrangements. The storage node arrangements need not be sequential oradjacent in some embodiments. Storage nodes 150 are hot pluggable,meaning that a storage node 150 can be inserted into a slot 142 in thechassis 138, or removed from a slot 142, without stopping or poweringdown the system. Upon insertion or removal of storage node 150 from slot142, the system automatically reconfigures in order to recognize andadapt to the change. Reconfiguration, in some embodiments, includesrestoring redundancy and/or rebalancing data or load.

Each storage node 150 can have multiple components. In the embodimentshown here, the storage node 150 includes a printed circuit board 158populated by a CPU 156, i.e., processor, a memory 154 coupled to the CPU156, and a non-volatile solid state storage 152 coupled to the CPU 156,although other mountings and/or components could be used in furtherembodiments. The memory 154 has instructions which are executed by theCPU 156 and/or data operated on by the CPU 156. As further explainedbelow, the non-volatile solid state storage 152 includes flash or, infurther embodiments, other types of solid-state memory.

Referring to FIG. 1, storage cluster 160 is scalable, meaning thatstorage capacity with non-uniform storage sizes is readily added, asdescribed above. One or more storage nodes 150 can be plugged into orremoved from each chassis and the storage cluster self-configures insome embodiments. Plug-in storage nodes 150, whether installed in achassis as delivered or later added, can have different sizes. Forexample, in one embodiment a storage node 150 can have any multiple of 4TB, e.g., 8 TB, 12 TB, 16 TB, 32 TB, etc. In further embodiments, astorage node 150 could have any multiple of other storage amounts orcapacities. Storage capacity of each storage node 150 is broadcast, andinfluences decisions of how to stripe the data. For maximum storageefficiency, an embodiment can self-configure as wide as possible in thestripe, subject to a predetermined requirement of continued operationwith loss of up to one, or up to two, non-volatile solid state storageunits 152 or storage nodes 150 within the chassis.

FIG. 2 is a block diagram showing a communications interconnect 170 andpower distribution bus 172 coupling multiple storage nodes 150.Referring back to FIG. 1, the communications interconnect 170 can beincluded in or implemented with the switch fabric 146 in someembodiments. Where multiple storage clusters 160 occupy a rack, thecommunications interconnect 170 can be included in or implemented with atop of rack switch, in some embodiments. As illustrated in FIG. 2,storage cluster 160 is enclosed within a single chassis 138. Externalport 176 is coupled to storage nodes 150 through communicationsinterconnect 170, while external port 174 is coupled directly to astorage node. External power port 178 is coupled to power distributionbus 172. Storage nodes 150 may include varying amounts and differingcapacities of non-volatile solid state storage 152 as described withreference to FIG. 1. In addition, one or more storage nodes 150 may be acompute only storage node as illustrated in FIG. 2. Authorities 168 areimplemented on the non-volatile solid state storages 152, for example aslists or other data structures stored in memory. In some embodiments theauthorities are stored within the non-volatile solid state storage 152and supported by software executing on a controller or other processorof the non-volatile solid state storage 152. In a further embodiment,authorities 168 are implemented on the storage nodes 150, for example aslists or other data structures stored in the memory 154 and supported bysoftware executing on the CPU 156 of the storage node 150. Authorities168 control how and where data is stored in the non-volatile solid statestorages 152 in some embodiments. This control assists in determiningwhich type of erasure coding scheme is applied to the data, and whichstorage nodes 150 have which portions of the data. Each authority 168may be assigned to a non-volatile solid state storage 152. Eachauthority may control a range of inode numbers, segment numbers, orother data identifiers which are assigned to data by a file system, bythe storage nodes 150, or by the non-volatile solid state storage 152,in various embodiments.

Every piece of data, and every piece of metadata, has redundancy in thesystem in some embodiments. In addition, every piece of data and everypiece of metadata has an owner, which may be referred to as anauthority. If that authority is unreachable, for example through failureof a storage node, there is a plan of succession for how to find thatdata or that metadata. In various embodiments, there are redundantcopies of authorities 168. Authorities 168 have a relationship tostorage nodes 150 and non-volatile solid state storage 152 in someembodiments. Each authority 168, covering a range of data segmentnumbers or other identifiers of the data, may be assigned to a specificnon-volatile solid state storage 152. In some embodiments theauthorities 168 for all of such ranges are distributed over thenon-volatile solid state storages 152 of a storage cluster. Each storagenode 150 has a network port that provides access to the non-volatilesolid state storage(s) 152 of that storage node 150. Data can be storedin a segment, which is associated with a segment number and that segmentnumber is an indirection for a configuration of a RAID (redundant arrayof independent disks) stripe in some embodiments. The assignment and useof the authorities 168 thus establishes an indirection to data.Indirection may be referred to as the ability to reference dataindirectly, in this case via an authority 168, in accordance with someembodiments. A segment identifies a set of non-volatile solid statestorage 152 and a local identifier into the set of non-volatile solidstate storage 152 that may contain data. In some embodiments, the localidentifier is an offset into the device and may be reused sequentiallyby multiple segments. In other embodiments the local identifier isunique for a specific segment and never reused. The offsets in thenon-volatile solid state storage 152 are applied to locating data forwriting to or reading from the non-volatile solid state storage 152 (inthe form of a RAID stripe). Data is striped across multiple units ofnon-volatile solid state storage 152, which may include or be differentfrom the non-volatile solid state storage 152 having the authority 168for a particular data segment.

If there is a change in where a particular segment of data is located,e.g., during a data move or a data reconstruction, the authority 168 forthat data segment should be consulted, at that non-volatile solid statestorage 152 or storage node 150 having that authority 168. In order tolocate a particular piece of data, embodiments calculate a hash valuefor a data segment or apply an inode number or a data segment number.The output of this operation points to a non-volatile solid statestorage 152 having the authority 168 for that particular piece of data.In some embodiments there are two stages to this operation. The firststage maps an entity identifier (ID), e.g., a segment number, inodenumber, or directory number to an authority identifier. This mapping mayinclude a calculation such as a hash or a bit mask. The second stage ismapping the authority identifier to a particular non-volatile solidstate storage 152, which may be done through an explicit mapping. Theoperation is repeatable, so that when the calculation is performed, theresult of the calculation repeatably and reliably points to a particularnon-volatile solid state storage 152 having that authority 168. Theoperation may include the set of reachable storage nodes as input. Ifthe set of reachable non-volatile solid state storage units changes theoptimal set changes. In some embodiments, the persisted value is thecurrent assignment (which is always true) and the calculated value isthe target assignment the cluster will attempt to reconfigure towards.This calculation may be used to determine the optimal non-volatile solidstate storage 152 for an authority in the presence of a set ofnon-volatile solid state storage 152 that are reachable and constitutethe same cluster. The calculation also determines an ordered set of peernon-volatile solid state storage 152 that will also record the authorityto non-volatile solid state storage mapping so that the authority may bedetermined even if the assigned non-volatile solid state storage isunreachable. A duplicate or substitute authority 168 may be consulted ifa specific authority 168 is unavailable in some embodiments.

With reference to FIGS. 1 and 2, two of the many tasks of the CPU 156 ona storage node 150 are to break up write data, and reassemble read data.When the system has determined that data is to be written, the authority168 for that data is located as above. When the segment ID for data isalready determined the request to write is forwarded to the non-volatilesolid state storage 152 currently determined to be the host of theauthority 168 determined from the segment. The host CPU 156 of thestorage node 150, on which the non-volatile solid state storage 152 andcorresponding authority 168 reside, then breaks up or shards the dataand transmits the data out to various non-volatile solid state storage152. The transmitted data is written as a data stripe in accordance withan erasure coding scheme. In some embodiments, data is requested to bepulled, and in other embodiments, data is pushed. In reverse, when datais read, the authority 168 for the segment ID containing the data islocated as described above. The host CPU 156 of the storage node 150 onwhich the non-volatile solid state storage 152 and correspondingauthority 168 reside requests the data from the non-volatile solid statestorage and corresponding storage nodes pointed to by the authority. Insome embodiments the data is read from flash storage as a data stripe.The host CPU 156 of storage node 150 then reassembles the read data,correcting any errors (if present) according to the appropriate erasurecoding scheme, and forwards the reassembled data to the network. Infurther embodiments, some or all of these tasks can be handled in thenon-volatile solid state storage 152. In some embodiments, the segmenthost requests the data be sent to storage node 150 by requesting pagesfrom storage and then sending the data to the storage node making theoriginal request.

In some systems, for example in UNIX-style file systems, data is handledwith an index node or inode, which specifies a data structure thatrepresents an object in a file system. The object could be a file or adirectory, for example. Metadata may accompany the object, as attributessuch as permission data and a creation timestamp, among otherattributes. A segment number could be assigned to all or a portion ofsuch an object in a file system. In other systems, data segments arehandled with a segment number assigned elsewhere. For purposes ofdiscussion, the unit of distribution is an entity, and an entity can bea file, a directory or a segment. That is, entities are units of data ormetadata stored by a storage system. Entities are grouped into setscalled authorities. Each authority has an authority owner, which is astorage node that has the exclusive right to update the entities in theauthority. In other words, a storage node contains the authority, andthat the authority, in turn, contains entities.

A segment is a logical container of data in accordance with someembodiments. A segment is an address space between medium address spaceand physical flash locations, i.e., the data segment number, are in thisaddress space. Segments may also contain metadata, which enable dataredundancy to be restored (rewritten to different flash locations ordevices) without the involvement of higher level software. In oneembodiment, an internal format of a segment contains client data andmedium mappings to determine the position of that data. Each datasegment is protected, e.g., from memory and other failures, by breakingthe segment into a number of data and parity shards, where applicable.The data and parity shards are distributed, i.e., striped, acrossnon-volatile solid state storage 152 coupled to the host CPUs 156 (SeeFIG. 5) in accordance with an erasure coding scheme. Usage of the termsegments refers to the container and its place in the address space ofsegments in some embodiments. Usage of the term stripe refers to thesame set of shards as a segment and includes how the shards aredistributed along with redundancy or parity information in accordancewith some embodiments.

A series of address-space transformations takes place across an entirestorage system. At the top are the directory entries (file names) whichlink to an inode. Inodes point into medium address space, where data islogically stored. Medium addresses may be mapped through a series ofindirect mediums to spread the load of large files, or implement dataservices like deduplication or snapshots. Medium addresses may be mappedthrough a series of indirect mediums to spread the load of large files,or implement data services like deduplication or snapshots. Segmentaddresses are then translated into physical flash locations. Physicalflash locations have an address range bounded by the amount of flash inthe system in accordance with some embodiments. Medium addresses andsegment addresses are logical containers, and in some embodiments use a128 bit or larger identifier so as to be practically infinite, with alikelihood of reuse calculated as longer than the expected life of thesystem. Addresses from logical containers are allocated in ahierarchical fashion in some embodiments. Initially, each non-volatilesolid state storage unit 152 may be assigned a range of address space.Within this assigned range, the non-volatile solid state storage 152 isable to allocate addresses without synchronization with othernon-volatile solid state storage 152.

Data and metadata is stored by a set of underlying storage layouts thatare optimized for varying workload patterns and storage devices. Theselayouts incorporate multiple redundancy schemes, compression formats andindex algorithms Some of these layouts store information aboutauthorities and authority masters, while others store file metadata andfile data. The redundancy schemes include error correction codes thattolerate corrupted bits within a single storage device (such as a NANDflash chip), erasure codes that tolerate the failure of multiple storagenodes, and replication schemes that tolerate data center or regionalfailures. In some embodiments, low density parity check (LDPC) code isused within a single storage unit. Reed-Solomon encoding is used withina storage cluster, and mirroring is used within a storage grid in someembodiments. Metadata may be stored using an ordered log structuredindex (such as a Log Structured Merge Tree), and large data may not bestored in a log structured layout.

In order to maintain consistency across multiple copies of an entity,the storage nodes agree implicitly on two things through calculations:(1) the authority that contains the entity, and (2) the storage nodethat contains the authority. The assignment of entities to authoritiescan be done by pseudo randomly assigning entities to authorities, bysplitting entities into ranges based upon an externally produced key, orby placing a single entity into each authority. Examples of pseudorandomschemes are linear hashing and the Replication Under Scalable Hashing(RUSH) family of hashes, including Controlled Replication Under ScalableHashing (CRUSH). In some embodiments, pseudo-random assignment isutilized only for assigning authorities to nodes because the set ofnodes can change. The set of authorities cannot change so any subjectivefunction may be applied in these embodiments. Some placement schemesautomatically place authorities on storage nodes, while other placementschemes rely on an explicit mapping of authorities to storage nodes. Insome embodiments, a pseudorandom scheme is utilized to map from eachauthority to a set of candidate authority owners. A pseudorandom datadistribution function related to CRUSH may assign authorities to storagenodes and create a list of where the authorities are assigned. Eachstorage node has a copy of the pseudorandom data distribution function,and can arrive at the same calculation for distributing, and laterfinding or locating an authority. Each of the pseudorandom schemesrequires the reachable set of storage nodes as input in some embodimentsin order to conclude the same target nodes. Once an entity has beenplaced in an authority, the entity may be stored on physical devices sothat no expected failure will lead to unexpected data loss. In someembodiments, rebalancing algorithms attempt to store the copies of allentities within an authority in the same layout and on the same set ofmachines.

Examples of expected failures include device failures, stolen machines,datacenter fires, and regional disasters, such as nuclear or geologicalevents. Different failures lead to different levels of acceptable dataloss. In some embodiments, a stolen storage node impacts neither thesecurity nor the reliability of the system, while depending on systemconfiguration, a regional event could lead to no loss of data, a fewseconds or minutes of lost updates, or even complete data loss.

In the embodiments, the placement of data for storage redundancy isindependent of the placement of authorities for data consistency. Insome embodiments, storage nodes that contain authorities do not containany persistent storage. Instead, the storage nodes are connected tonon-volatile solid state storage units that do not contain authorities.The communications interconnect between storage nodes and non-volatilesolid state storage units consists of multiple communicationtechnologies and has non-uniform performance and fault tolerancecharacteristics. In some embodiments, as mentioned above, non-volatilesolid state storage units are connected to storage nodes via PCIexpress, storage nodes are connected together within a single chassisusing Ethernet backplane, and chassis are connected together to form astorage cluster. Storage clusters are connected to clients usingEthernet or fiber channel in some embodiments. If multiple storageclusters are configured into a storage grid, the multiple storageclusters are connected using the Internet or other long-distancenetworking links, such as a “metro scale” link or private link that doesnot traverse the internet.

Authority owners have the exclusive right to modify entities, to migrateentities from one non-volatile solid state storage unit to anothernon-volatile solid state storage unit, and to add and remove copies ofentities. This allows for maintaining the redundancy of the underlyingdata. When an authority owner fails, is going to be decommissioned, oris overloaded, the authority is transferred to a new storage node.Transient failures make it non-trivial to ensure that all non-faultymachines agree upon the new authority location. The ambiguity thatarises due to transient failures can be achieved automatically by aconsensus protocol such as Paxos, hot-warm failover schemes, via manualintervention by a remote system administrator, or by a local hardwareadministrator (such as by physically removing the failed machine fromthe cluster, or pressing a button on the failed machine). In someembodiments, a consensus protocol is used, and failover is automatic. Iftoo many failures or replication events occur in too short a timeperiod, the system goes into a self-preservation mode and haltsreplication and data movement activities until an administratorintervenes in accordance with some embodiments.

As authorities are transferred between storage nodes and authorityowners update entities in their authorities, the system transfersmessages between the storage nodes and non-volatile solid state storageunits. With regard to persistent messages, messages that have differentpurposes are of different types. Depending on the type of the message,the system maintains different ordering and durability guarantees. Asthe persistent messages are being processed, the messages aretemporarily stored in multiple durable and non-durable storage hardwaretechnologies. In some embodiments, messages are stored in RAM, NVRAM andon NAND flash devices, and a variety of protocols are used in order tomake efficient use of each storage medium. Latency-sensitive clientrequests may be persisted in replicated NVRAM, and then later NAND,while background rebalancing operations are persisted directly to NAND.

Persistent messages are persistently stored prior to being transmitted.This allows the system to continue to serve client requests despitefailures and component replacement. Although many hardware componentscontain unique identifiers that are visible to system administrators,manufacturer, hardware supply chain and ongoing monitoring qualitycontrol infrastructure, applications running on top of theinfrastructure address virtualize addresses. These virtualized addressesdo not change over the lifetime of the storage system, regardless ofcomponent failures and replacements. This allows each component of thestorage system to be replaced over time without reconfiguration ordisruptions of client request processing.

In some embodiments, the virtualized addresses are stored withsufficient redundancy. A continuous monitoring system correlateshardware and software status and the hardware identifiers. This allowsdetection and prediction of failures due to faulty components andmanufacturing details. The monitoring system also enables the proactivetransfer of authorities and entities away from impacted devices beforefailure occurs by removing the component from the critical path in someembodiments.

FIG. 3 is a multiple level block diagram, showing contents of a storagenode 150 and contents of a non-volatile solid state storage 152 of thestorage node 150. Data is communicated to and from the storage node 150by a network interface controller (NIC) 202 in some embodiments. Eachstorage node 150 has a CPU 156, and one or more non-volatile solid statestorage 152, as discussed above. Moving down one level in FIG. 3, eachnon-volatile solid state storage 152 has a relatively fast non-volatilesolid state memory, such as nonvolatile random access memory (NVRAM)204, and flash memory 206. In some embodiments, NVRAM 204 may be acomponent that does not require program/erase cycles (DRAM, MRAM, PCM),and can be a memory that can support being written vastly more oftenthan the memory is read from. Moving down another level in FIG. 3, theNVRAM 204 is implemented in one embodiment as high speed volatilememory, such as dynamic random access memory (DRAM) 216, backed up byenergy reserve 218. Energy reserve 218 provides sufficient electricalpower to keep the DRAM 216 powered long enough for contents to betransferred to the flash memory 206 in the event of power failure. Insome embodiments, energy reserve 218 is a capacitor, super-capacitor,battery, or other device, that supplies a suitable supply of energysufficient to enable the transfer of the contents of DRAM 216 to astable storage medium in the case of power loss. The flash memory 206 isimplemented as multiple flash dies 222, which may be referred to aspackages of flash dies 222 or an array of flash dies 222. It should beappreciated that the flash dies 222 could be packaged in any number ofways, with a single die per package, multiple dies per package (i.e.multichip packages), in hybrid packages, as bare dies on a printedcircuit board or other substrate, as encapsulated dies, etc. In theembodiment shown, the non-volatile solid state storage 152 has acontroller 212 or other processor, and an input output (I/O) port 210coupled to the controller 212. I/O port 210 is coupled to the CPU 156and/or the network interface controller 202 of the flash storage node150. Flash input output (I/O) port 220 is coupled to the flash dies 222,and a direct memory access unit (DMA) 214 is coupled to the controller212, the DRAM 216 and the flash dies 222. In the embodiment shown, theI/O port 210, controller 212, DMA unit 214 and flash I/O port 220 areimplemented on a programmable logic device (PLD) 208, e.g., a fieldprogrammable gate array (FPGA). In this embodiment, each flash die 222has pages, organized as sixteen kB (kilobyte) pages 224, and a register226 through which data can be written to or read from the flash die 222.In further embodiments, other types of solid-state memory are used inplace of, or in addition to flash memory illustrated within flash die222.

Storage clusters 160, in various embodiments as disclosed herein, can becontrasted with storage arrays in general. The storage nodes 150 arepart of a collection that creates the storage cluster 160. Each storagenode 150 owns a slice of data and computing required to provide thedata. Multiple storage nodes 150 cooperate to store and retrieve thedata. Storage memory or storage devices, as used in storage arrays ingeneral, are less involved with processing and manipulating the data.Storage memory or storage devices in a storage array receive commands toread, write, or erase data. The storage memory or storage devices in astorage array are not aware of a larger system in which they areembedded, or what the data means. Storage memory or storage devices instorage arrays can include various types of storage memory, such as RAM,solid state drives, hard disk drives, etc. The storage units 152described herein have multiple interfaces active simultaneously andserving multiple purposes. In some embodiments, some of thefunctionality of a storage node 150 is shifted into a storage unit 152,transforming the storage unit 152 into a combination of storage unit 152and storage node 150. Placing computing (relative to storage data) intothe storage unit 152 places this computing closer to the data itself.The various system embodiments have a hierarchy of storage node layerswith different capabilities. By contrast, in a storage array, acontroller owns and knows everything about all of the data that thecontroller manages in a shelf or storage devices. In a storage cluster160, as described herein, multiple controllers in multiple storage units152 and/or storage nodes 150 cooperate in various ways (e.g., forerasure coding, data sharding, metadata communication and redundancy,storage capacity expansion or contraction, data recovery, and so on).

FIG. 4 shows a storage server environment, which uses embodiments of thestorage nodes 150 and storage units 152 of FIGS. 1-3. In this version,each storage unit 152 has a processor such as controller 212 (see FIG.3), an FPGA (field programmable gate array), flash memory 206, and NVRAM204 (which is super-capacitor backed DRAM 216, see FIGS. 2 and 3) on aPCIe (peripheral component interconnect express) board in a chassis 138(see FIG. 1). The storage unit 152 may be implemented as a single boardcontaining storage, and may be the largest tolerable failure domaininside the chassis. In some embodiments, up to two storage units 152 mayfail and the device will continue with no data loss.

The physical storage is divided into named regions based on applicationusage in some embodiments. The NVRAM 204 is a contiguous block ofreserved memory in the storage unit 152 DRAM 216, and is backed by NANDflash. NVRAM 204 is logically divided into multiple memory regionswritten for two as spool (e.g., spool_region). Space within the NVRAM204 spools is managed by each authority 512 independently. Each deviceprovides an amount of storage space to each authority 512. Thatauthority 512 further manages lifetimes and allocations within thatspace. Examples of a spool include distributed transactions or notions.When the primary power to a storage unit 152 fails, onboardsuper-capacitors provide a short duration of power hold up. During thisholdup interval, the contents of the NVRAM 204 are flushed to flashmemory 206. On the next power-on, the contents of the NVRAM 204 arerecovered from the flash memory 206.

As for the storage unit controller, the responsibility of the logical“controller” is distributed across each of the blades containingauthorities 512. This distribution of logical control is shown in FIG. 4as a host controller 402, mid-tier controller 404 and storage unitcontroller(s) 406. Management of the control plane and the storage planeare treated independently, although parts may be physically co-locatedon the same blade. Each authority 512 effectively serves as anindependent controller. Each authority 512 provides its own data andmetadata structures, its own background workers, and maintains its ownlifecycle.

FIG. 5 is a blade 502 hardware block diagram, showing a control plane504, compute and storage planes 506, 508, and authorities 512interacting with underlying physical resources, using embodiments of thestorage nodes 150 and storage units 152 of FIGS. 1-3 in the storageserver environment of FIG. 4. The control plane 504 is partitioned intoa number of authorities 512 which can use the compute resources in thecompute plane 506 to run on any of the blades 502. The storage plane 508is partitioned into a set of devices, each of which provides access toflash 206 and NVRAM 204 resources.

In the compute and storage planes 506, 508 of FIG. 5, the authorities512 interact with the underlying physical resources (i.e., devices).From the point of view of an authority 512, its resources are stripedover all of the physical devices. From the point of view of a device, itprovides resources to all authorities 512, irrespective of where theauthorities happen to run.

Each authority 512 has allocated or has been allocated one or morepartitions 510 of storage memory in the storage units 152, e.g.partitions 510 in flash memory 206 and NVRAM 204. Each authority 512uses those allocated partitions 510 that belong to it, for writing orreading user data. Authorities can be associated with differing amountsof physical storage of the system. For example, one authority 512 couldhave a larger number of partitions 510 or larger sized partitions 510 inone or more storage units 152 than one or more other authorities 512.

FIG. 6 is a system and action diagram showing distributed file deletion606 in a storage system. In this example, the storage system is embodiedin multiple blades 502, which could be installed in one or more chassis138 as depicted in FIG. 1, as a storage cluster 160. Each blade 502 hasa storage node 150 and one or more storage units 152. Each storage node150 has a processor 602 and one or more authorities 168 as describedabove with reference to FIGS. 1-5. Each storage unit has a processor604, NVRAM 204 and flash memory 206, also as described above.Distributed file deletion 606 can be embodied in further storageclusters and storage systems as readily devised in keeping with theteachings herein.

To delete a file, the client 608 sends a request 610, e.g., a request todelete the file, to the storage system. In some embodiments, the request610 is received by one of the storage nodes 150, which determines whichauthority 168 is the owner of the inode for the file, and forwards therequest 610 to the storage node 150 in which the inode owning authority168 resides. Various actions are shown in FIG. 6 under the file deletion606 process and at locations in the storage system, and denoted asforeground 612 or background 614 actions or tasks. A foreground task 612is one that should be performed in sequence, in parallel or in line withany actions that are visible to a client 608. A background task 614 isone that can be performed immediately, or later, but which does notnecessarily need to be performed prior to an action that is visible to aclient 608 (e.g., an acknowledgment, reply or other response to theclient 608). In action (1) (i.e., the circled “1”), the request 610 todelete a file is received, as a foreground task 614 taking place at anauthority 168 in a storage node 150, i.e., the authority 168 receivesthe request 610 from the client 608. More specifically, the processor602 in the storage node 150 in which the authority 168 resides receivesthe request 610 and performs actions on behalf of that authority 168.

In action (2), the authority 168 writes a “to do” list record, e.g. acleanup task list record, into NVRAM 204 in a storage unit 152, as aforeground task 614. In action (3), the authority 168 records a filedelete, i.e., a record of file deletion, in the NVRAM 204 in the storageunit 152, as a foreground task 614. In various embodiments, therecording of the file deletion, and the record of cleanup tasks to do,are persisted across the storage cluster, e.g., as redundant messages asdescribed above. After recording the file delete, action (4) commencesand the authority 168 that owns the inode of the file sends anacknowledgment 616, e.g., to acknowledge the file deletion, to theclient 608 as a foreground task 614. In some embodiments, the authority168 that owns the inode for the file also has responsibility for fileextents (i.e., file size as recorded in metadata, and reported to aclient 608 in response to a client inquiry) and records (e.g., inmetadata in NVRAM 204) any changes to the file extent.

As an internal response (i.e., a response internal to the storagesystem) to receiving the request 610, writing the “to do” list, and/orrecording the file deletion, various background tasks 612 are initiated.The authority 168 that owns the inode of the file determines theauthorities 168 that own the data portions of the file to be deleted, inan action (5) as a background task 612. The inode owning authority 168sends messages to these authorities 168, in an action (6) as abackground task 612. These messages are also persisted across thestorage cluster, e.g., as redundant messages as described above. Thestorage unit 152, or more specifically the processor 604 of that storageunit 152, flushes (i.e., transfers) the “to do” task list and the recordof the file deletion (recorded in NVRAM 204 in the actions (2) and (3))to the flash memory 206 of that storage unit 152, in the action (7), abackground task 612. In some embodiments the flushing is directed by theprocessor(s) 602 of the storage node(s) 150, at various time intervals,or in response to recording the file deletion so as to flush the recordof file deletion from NVRAM to flash memory and trigger background tasks612.

The authorities 168 that own the data portions of the file delete thevarious portions of the file, in batches, in the action (8), abackground task 612. In some embodiments, the creation and execution ofbatches or batch jobs of data deletion is triggered by the flush. Theremight be tens, hundreds or thousands or more pieces of the file, orpieces of further files from other file deletions or truncations, to bedeleted, and these can be batched up for deletion. This can be combinedwith garbage collection as a background task (see action (11)), in someembodiments. These authorities 168 then confirm the deletions, in anaction (9), as a background task 612. For example, the authorities 168that perform the data deletions send messages to the authority 168 thatowns the inode of the file. These messages are persisted with redundancyacross the storage system as described above, for robust recovery incase of failure in the storage system. Upon and responsive to receipt ofthe confirmations, for example as messages from the authorities 168performing the deletions, the authority 168 that owns the inode of thefile deletes the “to do” list (e.g., the cleanup “to do” task record),in the action (10), as a background task 612. Garbage collection, theaction (11), is also performed as a background task 612. In someembodiments, the background deletion of data, and garbage collection,are triggered by the flush, more specifically by the transfer of therecord of file deletion. By performing actual deletion of data, andrelated communication, preparatory and follow-up tasks as distributedbackground tasks 612 (i.e., distributed among many processors andcomponents of the storage system), the storage system can acknowledgethe file deletion request to the client 608 more quickly than if thesetasks were done in foreground.

FIG. 7 is a system and action diagram showing distributed filetruncation 702 in a storage system. Similarly to FIG. 6, in this examplethe storage system is embodied in multiple blades 502 with similarfeatures and contents, and distributed file truncation 702 can beembodied in further storage clusters and storage systems as readilydevised. To truncate a file, the client 608 sends a request 704, e.g., arequest to truncate the file, to the storage system. In someembodiments, the request 704 is received by one of the storage nodes150. That storage node 150, or more specifically the processor 602 inthe storage node 150, determines which authority 168 is the owner of theinode for the file, and forwards the request 704 to the storage node 150in which the inode owning authority 168 resides. Under the filetruncation 702 process, in action (1), the request 704 to truncate thefile is received by the authority 168, as a foreground task 612.

Still referring to FIG. 7, in action (2), the inode owning authority 168determines the authorities 168 that own the data portions of the filethat are to be deleted in the truncation, as a foreground task 612. Theinode owning authority 168 sends messages to those authorities 168, inthe action (3), as a foreground task 612. These authorities 168, invarious blades 502 and storage nodes 150, write truncation records totheir respective NVRAMs 204 in storage units 152, in the action (4).That is, each authority 168 that receives a message for truncating adata portion writes a truncation record to NVRAM 204, as a foregroundtask 612. These and other messages are persisted with redundancythroughout the storage system, as described above, for robust recoveryin case of failure. Each truncation record acts as an instruction toclear data in a specified range of addresses.

Continuing with FIG. 7, the authorities 168 reply, e.g., by sendingmessages, to the inode owning authority 168 after writing the truncationrecords, in the action (5), as a foreground task 612. Upon andresponsive to receiving such messages from all of the respondingauthorities 168, the inode owning authority 168 records the filetruncation in NVRAM 204 in the storage unit 152, in the action (6) as aforeground task 612. After recording the file truncation, the inodeowning authority 168 sends an acknowledgment 706, e.g., a message toacknowledge the file truncation, to the client 608, as a foreground task612. As an internal response to receiving the request 704 to truncatethe file, sending and/or receiving the messages, writing the truncationrecords, sending and receiving messages in reply to writing truncationrecords, and/or recording the file truncation, various background tasks614 are initiated. The truncation records and the record of the filetruncation are flushed (i.e., transferred) to flash memory 206 invarious storage units 152, in the action (8) as a background task 614,e.g., by the storage units 152 or more specifically their processors604. In some embodiments, this flush occurs at regular time intervals,and in other embodiments flushing is triggered by the recording of thefile truncation. In some embodiments, flushing the truncation record(s)triggers background deletion of data portions, and garbage collection.Authorities 168 that own the data portions to be deleted in the filetruncation do the deletions, in batches, in an action (9) as abackground task 612, similarly to what is done in the distributed filedeletion 606. In some embodiments, as above, the creation and executionof data deletion batches or batch jobs is triggered by the flush. Insome embodiments, the batches or batching combines deletion of dataportions from distributed file deletion 606 and distributed filetruncation 702, for multiple files and greater system efficiency.Garbage collection is performed as the action (10) in a background task614, which is combined with the batch data deletions in someembodiments. As above, in some embodiments garbage collection istriggered by the flush. By performing actual deletion of data as adistributed background task 612, the storage system can acknowledge thefile truncation request to the client 608 more quickly than if thesetasks were done in foreground.

In various versions, authorities 168 push information to otherauthorities 168, but they could also poll, or pull information fromauthorities 168. Once an inode owning authority 168 receivesconfirmation of receipt from other authorities 168 of data deletionmessages sent by the inode owning authority 168, there is robustness inthe system that cleanup will be completed even if there is a systemfailure. The receiving authorities 168 have taken responsibility, uponsending confirmation, and will clean up the file (i.e., perform thedirected, distributed data deletions), and the inode owning authority168 can persistently mark those regions of the files as deleted. Actualdeletion of the data portions proceeds in background, with garbagecollection eventually performing block erases to recover memory spacethat is freed up by the data deletions.

FIG. 8 is a flow diagram of a method for distributed file deletion andtruncation, which can be practiced in the storage cluster of FIGS. 1-7and further embodiments thereof, and in further storage systems. Some orall of the actions in the method can be performed by various processors,such as processors in storage nodes or processors in storage units. Inan action 802, a request for file deletion or truncation is receivedfrom a client. The request is received, in some embodiments, by anauthority that owns the inode for the file, e.g., by the processor in astorage node in which the authority resides. In an action 804, it isdetermined which authorities own data portions to be deleted. This maybe done by the inode owning authority, e.g., by the processor in thestorage node in which that authority resides. For file deletion, thisprocess or action can be done as a background task, since it is assumedthat all data portions of the file are to be deleted. For filetruncation, this process or action can be done as a foreground task,since the inode owning authority will need to wait for replies back fromthe authorities that will be deleting data portions, in someembodiments.

In an action 806, the file deletion or truncation is recorded. Thisaction is done by the inode owning authority, in some embodiments. Afterrecording the file deletion or truncation, the request is acknowledgedto the client, in the action 808. This is so that the file deletion ortruncation as recorded can be persisted, prior to acknowledging theclient, and this persisting assures that the file deletion or truncationwill be completed even if there is a failure and recovery in the system,making the acknowledgment to the client reliable. In an action 810, thedata portions are deleted, in background. With the above recording ofthe file deletion or truncation, and the persisting, the backgroundtasks can be picked up even if there is failure and recovery, and thatis why they need not be done in foreground.

The above method and variations thereof can be performed in otherstorage systems besides the storage cluster with storage nodes andstorage units described herein. It is the performance of deletion ofdata portions in background that allows the acknowledgment to be sent tothe client more quickly, reducing latency, as compared to performingdeletion of data portions in foreground. In variations, tasks discussedabove as operating in background could be moved to foreground, at a costof greater latency for the acknowledgment to the client. Tasks discussedabove as operating in foreground could be moved to background, at a costof reduced reliability and recoverability.

It should be appreciated that the methods described herein may beperformed with a digital processing system, such as a conventional,general-purpose computer system. Special purpose computers, which aredesigned or programmed to perform only one function may be used in thealternative. FIG. 9 is an illustration showing an exemplary computingdevice which may implement the embodiments described herein. Thecomputing device of FIG. 9 may be used to perform embodiments of thefunctionality for distributed file deletion and truncation in accordancewith some embodiments. The computing device includes a centralprocessing unit (CPU) 901, which is coupled through a bus 905 to amemory 903, and mass storage device 907. Mass storage device 907represents a persistent data storage device such as a disc drive, whichmay be local or remote in some embodiments. The mass storage device 907could implement a backup storage, in some embodiments. Memory 903 mayinclude read only memory, random access memory, etc. Applicationsresident on the computing device may be stored on or accessed via acomputer readable medium such as memory 903 or mass storage device 907in some embodiments. Applications may also be in the form of modulatedelectronic signals modulated accessed via a network modem or othernetwork interface of the computing device. It should be appreciated thatCPU 901 may be embodied in a general-purpose processor, a specialpurpose processor, or a specially programmed logic device in someembodiments.

Display 911 is in communication with CPU 901, memory 903, and massstorage device 907, through bus 905. Display 911 is configured todisplay any visualization tools or reports associated with the systemdescribed herein. Input/output device 909 is coupled to bus 905 in orderto communicate information in command selections to CPU 901. It shouldbe appreciated that data to and from external devices may becommunicated through the input/output device 909. CPU 901 can be definedto execute the functionality described herein to enable thefunctionality described with reference to FIGS. 1-8. The code embodyingthis functionality may be stored within memory 903 or mass storagedevice 907 for execution by a processor such as CPU 901 in someembodiments. The operating system on the computing device may beMS-WINDOWS™, UNIX™, LINUX™, iOS™, CentOS™, Android™, Redhat Linux™,z/OS™, or other known operating systems. It should be appreciated thatthe embodiments described herein may also be integrated with avirtualized computing system implemented with physical computingresources.

It should be understood that although the terms first, second, etc. maybe used herein to describe various steps or calculations, these steps orcalculations should not be limited by these terms. These terms are onlyused to distinguish one step or calculation from another. For example, afirst calculation could be termed a second calculation, and, similarly,a second step could be termed a first step, without departing from thescope of this disclosure. As used herein, the term “and/or” and the “/”symbol includes any and all combinations of one or more of theassociated listed items.

As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”,“comprising”, “includes”, and/or “including”, when used herein, specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof. Therefore, the terminology usedherein is for the purpose of describing particular embodiments only andis not intended to be limiting.

It should also be noted that in some alternative implementations, thefunctions/acts noted may occur out of the order noted in the figures.For example, two figures shown in succession may in fact be executedsubstantially concurrently or may sometimes be executed in the reverseorder, depending upon the functionality/acts involved.

With the above embodiments in mind, it should be understood that theembodiments might employ various computer-implemented operationsinvolving data stored in computer systems. These operations are thoserequiring physical manipulation of physical quantities. Usually, thoughnot necessarily, these quantities take the form of electrical ormagnetic signals capable of being stored, transferred, combined,compared, and otherwise manipulated. Further, the manipulationsperformed are often referred to in terms, such as producing,identifying, determining, or comparing. Any of the operations describedherein that form part of the embodiments are useful machine operations.The embodiments also relate to a device or an apparatus for performingthese operations. The apparatus can be specially constructed for therequired purpose, or the apparatus can be a general-purpose computerselectively activated or configured by a computer program stored in thecomputer. In particular, various general-purpose machines can be usedwith computer programs written in accordance with the teachings herein,or it may be more convenient to construct a more specialized apparatusto perform the required operations.

A module, an application, a layer, an agent or other method-operableentity could be implemented as hardware, firmware, or a processorexecuting software, or combinations thereof. It should be appreciatedthat, where a software-based embodiment is disclosed herein, thesoftware can be embodied in a physical machine such as a controller. Forexample, a controller could include a first module and a second module.A controller could be configured to perform various actions, e.g., of amethod, an application, a layer or an agent.

The embodiments can also be embodied as computer readable code on anon-transitory computer readable medium. The computer readable medium isany data storage device that can store data, which can be thereafterread by a computer system. Examples of the computer readable mediuminclude hard drives, network attached storage (NAS), read-only memory,random-access memory, CD-ROMs, CD-Rs, CD-RWs, magnetic tapes, and otheroptical and non-optical data storage devices. The computer readablemedium can also be distributed over a network coupled computer system sothat the computer readable code is stored and executed in a distributedfashion. Embodiments described herein may be practiced with variouscomputer system configurations including hand-held devices, tablets,microprocessor systems, microprocessor-based or programmable consumerelectronics, minicomputers, mainframe computers and the like. Theembodiments can also be practiced in distributed computing environmentswhere tasks are performed by remote processing devices that are linkedthrough a wire-based or wireless network.

Although the method operations were described in a specific order, itshould be understood that other operations may be performed in betweendescribed operations, described operations may be adjusted so that theyoccur at slightly different times or the described operations may bedistributed in a system which allows the occurrence of the processingoperations at various intervals associated with the processing.

In various embodiments, one or more portions of the methods andmechanisms described herein may form part of a cloud-computingenvironment. In such embodiments, resources may be provided over theInternet as services according to one or more various models. Suchmodels may include Infrastructure as a Service (IaaS), Platform as aService (PaaS), and Software as a Service (SaaS). In IaaS, computerinfrastructure is delivered as a service. In such a case, the computingequipment is generally owned and operated by the service provider. Inthe PaaS model, software tools and underlying equipment used bydevelopers to develop software solutions may be provided as a serviceand hosted by the service provider. SaaS typically includes a serviceprovider licensing software as a service on demand. The service providermay host the software, or may deploy the software to a customer for agiven period of time. Numerous combinations of the above models arepossible and are contemplated.

Various units, circuits, or other components may be described or claimedas “configured to” perform a task or tasks. In such contexts, the phrase“configured to” is used to connote structure by indicating that theunits/circuits/components include structure (e.g., circuitry) thatperforms the task or tasks during operation. As such, theunit/circuit/component can be said to be configured to perform the taskeven when the specified unit/circuit/component is not currentlyoperational (e.g., is not on). The units/circuits/components used withthe “configured to” language include hardware—for example, circuits,memory storing program instructions executable to implement theoperation, etc. Reciting that a unit/circuit/component is “configuredto” perform one or more tasks is expressly intended not to invoke 35U.S.C. 112, sixth paragraph, for that unit/circuit/component.Additionally, “configured to” can include generic structure (e.g.,generic circuitry) that is manipulated by software and/or firmware(e.g., an FPGA or a general-purpose processor executing software) tooperate in manner that is capable of performing the task(s) at issue.“Configured to” may also include adapting a manufacturing process (e.g.,a semiconductor fabrication facility) to fabricate devices (e.g.,integrated circuits) that are adapted to implement or perform one ormore tasks.

The foregoing description, for the purpose of explanation, has beendescribed with reference to specific embodiments. However, theillustrative discussions above are not intended to be exhaustive or tolimit the invention to the precise forms disclosed. Many modificationsand variations are possible in view of the above teachings. Theembodiments were chosen and described in order to best explain theprinciples of the embodiments and its practical applications, to therebyenable others skilled in the art to best utilize the embodiments andvarious modifications as may be suited to the particular usecontemplated. Accordingly, the present embodiments are to be consideredas illustrative and not restrictive, and the invention is not to belimited to the details given herein, but may be modified within thescope and equivalents of the appended claims.

What is claimed is:
 1. A method, comprising: determining, by anauthority of a plurality of authorities that owns an inode of a file,which authorities own data portions to be deleted, responsive to arequest for file deletion, wherein each authority of the plurality ofauthorities, including the authority owning the inode of the file andthe authorities that own the data portions to be deleted, is configuredto own inodes of files and entire files and own data portions of furtherfiles associated with inodes owned by other authorities; recording, bythe authority owning the inode, the requested file deletion in a firstmemory, and providing an acknowledgement to the request for filedeletion in response to the recording; transferring, by the authorityowning the inode, the recorded file deletion from the first memory to asecond memory to enable the authorities that own the data portions to bedeleted to generate batch data deletions as a background process, thesecond memory comprising persistent memory to persist the recorded filedeletion; and deleting, in the background by the authorities that ownthe data portions to be deleted, wherein the deleting is performedresponsive to the transferring and based on the batch data deletions. 2.The method of claim 1, further comprising: sending messages regardingthe data portions to be deleted from the authority owning the inode tothe authorities that own the data portions to be deleted, wherein theauthority owning the inode is identified through a hash algorithmapplied to the inode.
 3. The method of claim 1, wherein the determiningis performed in the background and the recording is performed inforeground, for file deletion, and further comprising: recording arecord of cleanup tasks in the first memory.
 4. The method of claim 1,further comprising: triggering garbage collection, based on thetransferring.
 5. The method of claim 1, wherein the deleting comprises:collecting data portions to be deleted for deletion as batches of dataportions.
 6. A tangible, non-transitory, computer-readable media havinginstructions thereupon which, when executed by a processor, cause theprocessor to perform a method comprising: receiving a request fordeletion or truncation of a file by an authority of a plurality ofauthorities that owns an inode of the file; writing a record to a firstmemory indicating the requested deletion of the file and providing anacknowledgement to the request for file deletion in response to thewriting, the writing executed in foreground by the authority owning theinode of the file, wherein ownership of the inode is assigned prior towriting the file; transferring the recorded file deletion from the firstmemory to a second memory by the authority owning the inode to enablethe authorities that own the data portions to be deleted to generatebatch data deletions as a background process, the second memorycomprising persistent memory to persist the recorded file deletionwherein each authority, including the authority owning the inode of thefile and the authorities that own the data portions to be deleted, isconfigured to own inodes of files and entire files and own data portionsof further files associated with inodes owned by other authorities; anddeleting data portions of the file, in the background, by the pluralityof authorities each owning one or more of the data portions to bedeleted, wherein the deleting is performed responsive to thetransferring and based on the batch data deletions.
 7. Thecomputer-readable media of claim 6, wherein the method furthercomprises: acknowledging the deletion of the file to a client by theauthority owning the inode in the foreground, responsive to the writingthe record to the first memory, wherein the authority owning the inodeis identified through a hash algorithm applied to the inode.
 8. Thecomputer-readable media of claim 6, wherein the method furthercomprises: receiving replies from the plurality of authorities in theforeground, wherein the writing the record to the first memory isindicating the deletion of the file and is responsive to the receivingthe replies.
 9. The computer-readable media of claim 6, wherein themethod further comprises: performing garbage collection in the secondmemory, triggered by the transferring.
 10. The computer-readable mediaof claim 6, wherein the method further comprises: writing a truncationrecord to the first memory, by each of the plurality of authoritiesowning one or more of the data portions, the truncation record acting asan instruction to clear data in a specified range of addresses,responsive to a request being for truncation of the file.
 11. Thecomputer-readable media of claim 6, wherein the method furthercomprises: writing a cleanup record to the first memory, in theforeground, by the authority owning the inode of the file, responsive tothe request being for the deletion of the file.
 12. A storage system,comprising: a first memory, distributed in the storage system and havingRAM (random-access memory) configurable to hold metadata; a secondmemory, distributed in the storage system and having solid-state storagememory, configurable to hold data and metadata; a plurality ofprocessors, configured to record in the first memory, by an authority ofa plurality of authorities that owns an inode of a file, deletion of thefile, responsive to a request for the deletion of the file and providingan acknowledgement to the request for file deletion in response to therecording, wherein ownership of the inode is assigned prior to writingthe file; the plurality of processors further configurable to record inthe first memory, by the authority that owns the inode of a furtherfile, truncation of the further file, responsive to a request for thetruncation of the further file; the plurality of processors furtherconfigurable to transfer the recorded file deletion from the firstmemory to the second memory by the authority owning the inode of thefile to enable the authorities that own the data portions to be deletedto generate batch data deletions as a background process, wherein thesecond memory persists the recorded file deletion and wherein eachauthority, including the authority owning the inode of the file and theauthorities that own the data portions to be deleted, is configured toown inodes of files and entire files and own data portions of furtherfiles associated with inodes owned by other authorities; and theplurality of processors further configured to have the plurality ofauthorities, each authority of the plurality of authorities that owns adata portion to be deleted, delete the data portions in the secondmemory, in the background, resulting from the request for the deletionof the file, wherein the deleting is performed responsive to thetransferring and based on the batch data deletions.
 13. The storagesystem of claim 12, further comprising: the plurality of processorsfurther configurable to have the authority that owns the inode of thefile send messages, in the background, to the authorities that own thedata portions to be deleted resulting from the request for the deletionof the file, wherein the authority owning the inode is identifiedthrough a hash algorithm applied to the inode.
 14. The storage system ofclaim 12, further comprising: the plurality of processors furtherconfigurable to have the authority that owns the inode of the furtherfile send messages, in foreground, to the authorities that own the dataportions to be deleted resulting from the request for the truncation ofthe further file, wherein to record in the first memory truncation ofthe further file is responsive to replies from the authorities that ownthe data portions to be deleted for the truncation of the further file.15. The storage system of claim 12, further comprising: the plurality ofprocessors further configured to trigger garbage collection in thesecond memory responsive to the transferring.
 16. The storage system ofclaim 12, wherein to have the plurality of authorities delete the dataportions in the second memory comprises: the plurality of processorsfurther configurable to have the plurality of authorities performbackground cleanup work in batches.
 17. The storage system of claim 12,wherein to have the plurality of authorities delete the data portions inthe second memory resulting from the request for the truncation of thefurther file comprises: the plurality of processors further configurableto have each of the plurality of authorities that owns a data portion tobe deleted for the truncation of the further file, write a truncationrecord to the first memory and reply back to the authority that owns theinode of the further file, in foreground.